The present invention relates generally to a shower pipe assembly for spraying a liquid, particularly to shower pipe assembly for use as a washer or spraying device, and more particularly to a shower pipe assembly for washer devices comprising rotary drum filters.
Devices for spraying liquids such as washing fluids are well known in the prior art. For example, conventional washer devices include pressure washers and belt washers. Other known washer devices are rotary drum filters are commonly used in the pulp and paper industry for dewatering and washing a pulp slurry. Such filters include a rotary drum partially submerged in a tank of pulp slurry. The drum surface is conventionally covered by a filter screen. As the screen rotates through the pulp slurry, a vacuum is applied within a portion of the drum, collecting a wet mat of fibers from the slurry on the screen. As the screen emerges from the tank, slurry liquid or filtrate is drawn inwardly through the screen by the vacuum and discharged through suitable piping, thereby removing the liquid from the mat. Examples of such filters are disclosed generally in U.S. Pat. No. 4,276,169 to Browne, et al., U.S. Pat. No. 4,248,716 to LaValley, U.S. Pat. No. 4,370,231 to LaValley, and in the patents cited therein.
Conventionally, about half a dozen parallel shower pipes are angularly spaced around a segment of the drum extending from just above the surface of the slurry to the top of the drum, proceeding in the direction of drum rotation. These pipes extend axially of the drum and are supported adjacent the ends of the drum. Washing liquid is discharged in a spray from the shower pipes to wash the pulp fibers as the mat emerges from the slurry. The pipes are spaced a fixed radial distance from the filter screen. This distance is preferably constant along the length of the pipes so that spray intensity and distribution are substantially uniform all the way across the mat. Examples of such shower pipes are disclosed in U.S. Pat. Nos. 3,150,082 to Rich and 3,363,774 to Luthi.
One persistent problem in the design and manufacture of rotary drum filters for use in pulp manufacture is the mitigation of corrosion. This problem has been overcome in part by making as many components of the filters as possible of corrosion-resistant material, such as fiberglass reinforced plastic. However, some prior attempts at making shower pipes of fiberglass reinforced plastic have suffered from several drawbacks.
One drawback is a tendency of the pipes to sag. Conventional drum filters are very long, often 20 feet or more. To span the length of the drum, the shower pipes must be even longer. Such pipes are ordinarily supported only at their ends and, during operation, are filled with washing liquid. Consequently, they must be extremely stiff to minimize sagging between their ends. Prior shower pipes, constructed of fiberglass reinforced plastic alone and having a cylindrical cross section, are not sufficiently stiff to resist sagging.
Therefore, to increase stiffness in the vertical plane, it has been proposed to provide such pipes with a vertical fin or "stiff back" along one side. However, each pipe must be rotationally positioned so that its spray outlets or nozzles direct the spray against the mat at about the same angle of incidence. The rotational position thus varies with the angular position of each pipe around the drum. Applying a stiff back on all pipes in the same position relative to the spray outlets would defeat the purpose of the stiff back in the pipes that are rotationally positioned with stiff back approaching horizontal. Depending on pipe spacing, such positioning might also be precluded by interference between the stiff back of one pipe and an adjacent pipe. Hence, to be effective, this proposal would require making a different configuration pipe for each angular position around the drum.
Various shower pipe designs having steel angle members or stiffeners imbedded in the plastic at angular intervals around the pipe have also been tried, but still sag unacceptably. In one example, a 17 foot long cylindrical shower pipe, reinforced with three steel angle members, exhibited substantial sag when supporting a static load of 100 pounds midway between its ends.
Another problem involves the spray pattern of washing liquid discharged from the shower pipes. It is desirable to wash the mat uniformly, necessitating continuous spray coverage along the axial length of the drum. However, since the mat is typically thin and fragile, care must be taken to avoid tearing it with excessive localized spray intensity. Accordingly, a variety of different spraying arrangements have been proposed. One such arrangement uses a single row of spray holes spaced along the length of the pipe, together with some means for diffusing the spray from each hole to provide overlapping coverage. One form of diffusing means is a continuous lip or flange positioned along the row of holes and extending outwardly from the pipe to cause the spray from each hole to fan out. This approach is unsatisfactory because it concentrates too much spray pressure where overlapping adjacent fans of spray both strike the mat, often tearing the mat. Other forms of diffusing means include a whistle-type nozzle and a spoon-type diffuser positioned alongside each spray outlet. The latter forms of spray diffusers have also been tried in conjunction with double rows of longitudinally staggered holes. However, in practice, they do not provide sufficiently uniform spray coverage and are susceptible to plugging, particularly by fiber back-spattering from the mat into the spray outlets by the spray. Changing the size of these nozzles does not substantially change the flow rate of the spray stream.
An additional disadvantage is the difficulty of making the foregoing shower pipe designs of fiberglass reinforced plastic using conventional manufacturing techniques. Heretofore, fiberglass reinforced plastic washer pipes have been formed on a cylindrical mandrel. Once a cylindrical pipe is formed, steel stiffeners are applied to its outer surface and overlain with additional fiberglass reinforced plastic material. Next, cylindrical spray holes are drilled in a row along a side of the pipe. Finally, a diffuser flange is positioned along the row of holes and secured to the pipe. This process produces a pipe having a rough and uneven outer surface. Such a surface precludes accurate positioning of the diffuser flange relative to the row of holes, thereby causing uneven diffusion of the spray. This process also renders virtually impossible the formation of complex shapes of spray holes or nozzles. And the resultant product has the functional drawbacks described above, namely, sagging and taring the mat.
Many of the foregoing problems are eliminated by the shower pipes manufactured by LaValley Industries, Inc., the assignee of the entire interest in this application, which are described in U.S. Pat. No. 4,522,716, U.S. Pat. No. 4,670,099, U.S. Pat. No. 4,697,292 and U.S. Pat. No. 4,795,558. For example, in U.S. Pat. No. 4,522,716, the shower pipe is made of fiberglass reinforced plastic and has a rectangular cross-section providing substantial rigidity against sagging between the ends of the pipe regardless of the rotational orientation of the pipe along a rotary drum filter. The pipe is stiffened by a pair of structural connecting flanges which extend along opposite sides of the pipe and provide rigidity to prevent the pipe from sagging. The pipe also includes reinforcing rods which extend along the interior corners of the pipe, also to provide rigidity against sagging.
Such pipes are preferably formed by molding them in channel-shaped half sections which are subsequently joined together along their connecting flanges. Spray holes are machined in one of the half sections in two parallel rows in which the holes of one row are staggered from the holes of the other row. Continuous diffusion members extend along each row so as to diffuse the discharges of liquid from each row of holes into two different planes. In this way, overlapping spray coverage is obtained without any overconcentration of spray at any point on the mat. The spray holes have a constricting frustoconical shape to better diffuse the discharge of liquid onto the diffusion members.
Although the LaValley shower pipe of U.S. Pat. No. 4,522,716 is a great improvement over known prior shower pipes, its integral essentially all fiberglass construction is laborious and expensive to manufacture, and requires laborious machining of each spray hole. Furthermore, while the continuous diffusion flanges along each row of spray holes are an improvement over prior hole-diffuser arrangements, the diffusion pattern they produce leaves room for more improvement.
U.S. Pat. No. 4,795,558, which is assigned to the common assignee of this application and is incorporated herein by reference, is directed to a rigid elongate pipe made of fiberglass-reinforced plastic. Spray holes extend in spaced apart relationship axially along the pipe, the holes extending through an outer wall of the pipe for discharging a liquid spray line along the length of the pipe when it is filled with a liquid under pressure. The pipe is generally fabricated in two channel-shaped half sections bonded together along flanges to define a pipe of rectangular section with structural rigidifying flanges extending along opposite sides. The pipe may also be fabricated in two angle-shaped half sections bonded together along flanges also to define a pipe of rectangular section, but with structural rigidifying flanges at diagonally opposite corners.
The individual diffusion flanges set forth in the U.S. Pat. No. 4,795,588 patent, are internally-mounted. In providing the requisite diffused flange member-containing shower pipes (see FIGS. 8 and 10 of U.S. Pat. No. 4,795,558) the frustoconical spray holes and associated diffusion flanges are formed as separate preformed injection-molded plastic members 148, 146 which are assembled together at corresponding straight-bored holes 145 through bottom wall 122 of the lower pipe section before the two pipe sections are joined together. A primary reason for employing the respective two-pipe sections is to enable attachment of plastic members 148 and 146 one to the other. More specifically, member 146 is a diffusion lip or flange which extends from the outside or underside of pipe 110. Member 148 comprises a hollow insert nut, which includes an enlarged hex head 150 joined to an externally threaded shank 152, seats against the inside surface of bottom wall 122, and threadingly engages internal threads 160 on shank 152 of insert 148. Therefore, one must have access to the internal portion of bottom wall 122 in order to join members 148 and 146 together. However, the use of a two-piece body causes certain problems. First, it is more expensive to built a two-piece body. Secondly, a two-piece body has approximately 20% the hydraulic burst pressure strength of a comparable one-piece body. Shower failure (burst) under pressure accounts for major problems in the shower pipe manufacturing business. When plastic members 148 and 146 are assembled, they are sonically welded together one to the other. Therefore, the pipe members are not readily separable so that any damage to diffusion flange members requires that the pipe section surrounding the damaged member be cut out of the pipe. The missing area is then replaced by patching in a new flange member and pipe section. This replacement operation is typically conducted by the customer. Since the customer is not familiar with the proper techniques for patching the replacement section, it takes up to about 2 hours to complete the patching operation. Patching also adversely affects the flow geometry of the new flange member since only a portion of the pipe underneath the flange member is replaced during that procedure. Replacement of the entire shower pipe, at an average cost to the customer of about $14,000, is needed when there is a change in the pulping production rate, or in the pulping process, or in governmental requirements. All of these changes require a corresponding change in the liquid flow rate from the flange member. This change can only be accomplished by the above-described shower pipe replacement.
Accordingly, there remains a need for a shower pipe which encompasses the improved features of U.S. Pat. No. 4,522,716, U.S. Pat. No. 4,670,099, U.S. Pat. No. 4,697,292, and U.S. Pat. No. 4,795,558, but which is capable of overcoming the above-described problems associated with those structures.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment which proceeds with reference to the drawings.